This invention relates to a process for the recovery of substantially pure .epsilon.-caprolactam from a contaminated aqueous .epsilon.-caprolactam solution.
Such a contaminated solution is obtained, for example, as the wash water obtained when a solution of caprolactam in an organic solvent is washed with water at a pH greater than 4.5, usually 7-9, as described in U.S. Pat. No. 3,850,910.
If a solution of caprolactam in an organic solvent, as obtained in the process according to U.S. Pat. No. 2,758,991, is washed with water at a pH of greater than 4.5, for example at a pH of 7-9, wash water containing contaminated caprolactam is obtained in addition to a solution of caprolactam in the solvent employed.
Although the amount of caprolactam in the wash water obtained from either process is small in relation to the amount of caprolactam dissolved in the organic solvent, we have observed that direct discharge of this caprolactam-laden solution greatly reduces the efficiency of the overall process and hence increases the cost. However, recycling this wash water back to the reaction mixture obtained in the rearrangement of cyclohexanone oxime to caprolactam by means of sulfuric acid, which is proposed in U.S. Pat. No. 3,850,910, according to one experience may adversely affect further processing.